Integrated Modelling of Plasmas in the ST40 High-Field Spherical Tokamak

The ST40 tokamak [1], built and operated by Tokamak Energy, has recently been upgraded with upper and lower divertors to enable double null diverted operations with up to 1MA of plasma current and 1.5MW of neutral beam heating. ST40 is a high field spherical tokamak (ST), B_T=3T at R₀=0.4-0.5m, A=1.6 – 1.9 with a goal to extend the high field ST physics basis. Crucially, transport and confinement in high field, high temperature STs will be explored in support of the design of future ST power plants [2]. Extensive modelling activities have been undertaken to support ST40 operations. Integrated data-analysis and modelling has been carried out on measurements from the recent experimental campaign for data and model validation. A range of plasma equilibrium in double-null configuration have been designed along with detailed scenario modelling, including 1.5D transport simulations and 2D SOL modelling. Gyrokinetic analysis has been performed to assess the level of expected turbulent transport. Building upon the NSTX pedestal database the pedestal width and height in the high performance ST40 scenarios have been predicted. MHD stability analysis and beta limit have been assessed. ST40 will be initially operated in hydrogen with up to 1.5 MW of NBI (0.8MW at 55kV and 0.7MW at 25kV). ST40 will be upgraded in view of the follow up Programme in deuterium, with 2MW of 55kV NBI and around 1.6MW 105/140GHz ECRH, and a new inner vacuum vessel and PFCs. Careful analysis of the power deposited in the divertor during high performance operation has also been carried out.

[1] M. Gryaznevich, O. Asunta (2017) Fusion Eng. Des. 123 177-180

[2] P F Buxton et al (2019) Plasma Phys. Control. Fusion 61 035006